Oxygen vacancy formation and migration in ceria is central to its performance as an ionic conductor. Ceria doped with suitable aliovalent dopants has enhanced oxygen ion conductivity – higher than that of yttria stabilized zirconia (YSZ), the most widely used electrolyte material in solid oxide fuel cells (SOFC). To gain insight into atomic defect migration in this class of promising electrolyte materials, we have performed total energy calculations within the framework of density functional theory (DFT+U) to study oxygen vacancy migration in ceria, Pr-doped ceria (PDC) and Gd-doped ceria (GDC). We report activation energies for various oxygen vacancy migration pathways in PDC and GDC. Results pertaining to the preferred oxygen vacancy formation sites and migration pathways in these materials will be discussed in detail. Overall, the presence of Pr and Gd ions significantly affects oxygen vacancy formation and migration, in a complex manner requiring the investigation of many different migration events. We propose a relationship that explains the role of additional dopants in lowering the activation energy for vacancy migration in PDC and GDC.

Proton conducting ceramics are considered as promising membranes for medium temperature fuel cells, water stream electrolyzers and CO2/syngas converters. Materials for these applications have to be mechanically and chemically stable at corrosive conditions of temperature and water vapor pressure in order to ensure the long life-time operation. Our comprehensive Raman, infrared, thermogravimetric, thermal expansion and neutron diffraction studies have shown that the choice of A and B elements as well as the material processing (synthesis, geometry, density, etc.) are crucial to control aging of material. We will consider an example of BaZr0.25In0.75O3 perovskite to show that several factors such as the carbonation, the traces of secondary AO phases at the grain boundaries as well as the use of samples with highly active surface, i.e. powders or lightly densified ceramics can cause: i) preferential adsorption of surface protonic species such as hydroxides, (hydro)carbonates, water, ii) decreased incorporation of bulk protonic species responsible for the proton conduction, iii) significant modification of the host perovskite structure up to complete crumbling of the material. We will show how to improve potential application of perovskites by understanding and controlling these processes.

Nanoparticle catalyst of PtRuAu/C for direct methanol fuel cell anodes was synthesized by a radiolytic process. Its methanol oxidation activity and the electrochemical durability were evaluated by using the linear sweep voltammetry and the cyclic voltammety. The Au addition significantly improved the durability in comparison with PtRu/C catalyst without losing its high activity. The atomic structure was characterized with techniques of the transmission electron microscopy, the X-ray diffraction, the X-ray fluorescence spectroscopy and the X-ray absorption fine structure. These results implied that the arrangement of Pt and Ru atoms in the PtRuAu/C has no significant difference from that without Au, possessing a structure of Pt rich core and PtRu alloy shell. We concluded that the improvement in durability could originate from these PtRu nanoparticles decorated with Au, but not from particles with high Au contents.

Stable, catalytically active, and inexpensive halogen electrodes are essential for the success of the regenerative hydrogen-halogen fuel cell as a competitive means of large-scale electricity storage. We report the synthesis and electrochemical testing of two novel electrode materials — ruthenium-cobalt and ruthenium-manganese alloy oxides. These alloys were fabricated by wet chemical synthesis methods as a coating on a titanium metal substrate and tested for chloride and bromide oxidation and for chlorine and bromine reduction. These alloy oxides exhibit high catalytic potency and good electrical conductivity good stability, while having a significantly reduced precious metal composition compared to commercial chloride oxidation electrodes made of the oxide of a ruthenium-titanium alloy. We tested alloys with Ru content as low as 1% that maintained good electrochemical activity. Stability tests indicate immeasurably small mass loss.

In this work, we investigated the electrocatalytic oxygen reduction reaction (ORR) activity of vertically aligned, single-layer, carbon-free, and single crystal Pt nanorod arrays utilizing cyclic voltammetry (CV) and rotating-disk electrode (RDE) techniques. A glancing angle deposition (GLAD) technique was used to fabricate 200 nm long Pt nanorods, which corresponds to Pt loading of 0.16 mg/cm2, on glassy carbon (GC) electrode at a glancing angle of 85° as measured from the substrate normal. An electrode comprised of conventional carbon-supported Pt nanoparticles (Pt/C) was also prepared for comparison with the electrocatalytic ORR activity and stability of Pt nanorods. CV results showed that the Pt nanorod electrocatalyst exhibits a more positive oxide reduction peak potential compared to Pt/C, indicating that GLAD Pt nanorods are less oxophilic. In addition, a series of CV cycles in acidic electrolyte revealed that Pt nanorods are significantly more stable against electrochemically-active surface area loss than Pt/C. Moreover, room temperature RDE results demonstrated that GLAD Pt nanorods exhibit higher area-specific ORR activity than Pt/C. The enhanced electrocatalytic ORR activity of Pt nanorods is attributed to their larger crystallite size, single-crystal property, and the dominance of (110) crystal planes on the large surface area nanorods sidewalls, which has been found to be the most active plane for ORR. However, the Pt nanorods showed lower mass specific activity than the Pt/C electrocatalyst due to the large diameter of the Pt nanorods.

In this study, platinum was electroplated onto bare Ti substrates (Pt black) and through a porous AAO membrane (Pt nanowires). The morphology of the deposits was observed by scanning electron microscopy. Preferential orientation along the (100) direction into the bulk material was evidenced through XRD analysis, as well as at the nanowire surface by using electrochemical characterization. These highly oriented Pt nanowires exhibited an increased activity for the electrocatalytic oxidation of hydrazine oxidation, as compared to Pt black.

Nonadiabatic energy dissipation by electron subsystem of nanostructured solids unveil interesting opportunities for the solid-state energy conversion and sensor applications. We found that planar Pd/n-SiC, Pt/n-GaP and Pd/n-GaP Schottky structures with nanometer thickness metallization demonstrates a nonadiabatic channel for the conversion into electricity the energy of a catalytic hydrogen-to-water oxidation process on the metal layer surface. The observed abovethermal current greatly complements the usual thermionic emission current, and its magnitude is linearly proportional to the rate of formation and desorption of product water molecules from the nanostructure surface. The possibilities and advantages of utilizing the nonadiabatic functionality in a novel class of chemical-to-electrical energy conversion devices are discussed. The technology has a potential for a very high volumetric energy density due to the intrinsically planar device architecture.

Hydrogen was converted to such a material as coal or oil with a low specific gravity so that it could be stored for a longer period and transported for a long distance at room temperature and under atmospheric pressure; which is sodium metal or sodium hydride. Sodium metal is produced with molten-salt electrolysis from seawater by wind power and transported to a thermoelectric power station in the consumption place for hydrogen-fueled combustion power generation. Sodium hydroxide, a waste, is re-electrolyzed to produce sodium for hydrogen generation; which constructs a hydrogen fuel cycle. This hydrogen fuel cycle is a clean, environmentally friendly recycle system that never requires repeated supply of raw materials in the same manner as the nuclear fuel cycle. Sodium or sodium hydride is an alternative energy.

Catalysts in which Pt and Cu are immobilized on support particles of γ-Fe2O3 were synthesized by the radiolytic process and were evaluated for CO oxidation in a gas flow mixture (1% CO, 0.5% O2, 67.2% H2 and N2 balance) by measuring the CO concentration in the outlet gas. The Pt/Cu atomic ratios of the as-synthesized catalysts were determined to be 100:0, 90:10, 78:22, 50:50, 21:79, and 11:89, and the total metal loadings determined by chemical analyses were 10 wt%. Material characterization was performed using X-ray diffraction, X-ray absorption near edge structure, and transmission electron microscopy, and it was indicated that the composite catalysts consist of Pt-Cu bimetallic grains immobilized on the support at higher Pt-loading, while CuO with poor crystallinity is also observed at lower Pt-loading. The catalytic activity decreased as the Pt-loading was decreased to 50 at%, and also with increasing temperature. However, as the Pt-loading was further decreased, the activity contrariwise increased, and increased with increasing temperature up to 100 °C. The sample containing only 11 at% Pt exhibited the highest activity at 100 °C, which is higher than that of the commercial catalyst measured for comparison, and given at a lower temperature than that for the commercial catalyst. This enhanced activity, despite the low Pt-loading, could be attributed to oxygen supply via CuO from the O2-poor atmosphere to PtCu bimetallic grains trapping CO molecules. This new material is promising for use as a catalyst to purify hydrogen gas fed to a polymer electrolyte fuel cell.